Remove a dead branch from ARGV.kegs

rack cannot be nil at the point where FormulaUnavailableError is raised,
so we don't need a branch to deal with that.

Library/Homebrew/extend/ARGV.rb

@@ -26,6 +26,7 @@ module HomebrewArgvExtension
       linked_keg_ref = HOMEBREW_REPOSITORY/"Library/LinkedKegs"/name
       opt_prefix = HOMEBREW_PREFIX/"opt"/name
 
+      begin
         if opt_prefix.symlink? && opt_prefix.directory?
           Keg.new(opt_prefix.resolved_path)
         elsif linked_keg_ref.symlink? && linked_keg_ref.directory?
@@ -37,17 +38,14 @@ module HomebrewArgvExtension
         else
           raise MultipleVersionsInstalledError.new(name)
         end
-    end
       rescue FormulaUnavailableError
-    if rack
         raise <<-EOS.undent
           Multiple kegs installed to #{rack}
           However we don't know which one you refer to.
           Please delete (with rm -rf!) all but one and then try again.
           Sorry, we know this is lame.
         EOS
-    else
-      raise
+      end
     end
   end